A flavoprotein. Unlike EC 1.6.5.2, NAD(P)H dehydrogenase (quinone), this quinone reductase cannot use NADH or NADPH; instead it uses N-ribosyl- and N-alkyldihydronicotinamides. Polycyclic aromatic hydrocarbons, such as benz[a]anthracene, and the oestrogens 17beta-estradiol and diethylstilbestrol are potent inhibitors, but dicoumarol is only a very weak inhibitor [2]. This enzyme can catalyse both 2-electron and 4-electron reductions, but one-electron acceptors, such as potassium ferricyanide, cannot be reduced [3].